Snap lock sheet-metal seam



Jan. 3, 1967 L. F. DEMMLER 3,295,560

SNAP LOCK SHEET-METAL sEAM Original Filed June 1, 1964 5 Sheets-Sheet 1 Q E k i l L4 /4 a .5 "4 30 3 E. 2 EL .3 30 9 20 2 2 9' 20 24 6 '5 7 I 7 27 7 2? a V 22 INVENTOR. 22 g 9 1g laws I. DEMML E2 H15 Arr euzv Jan. 3, 1967 1.. F. DEMMLER 3,295,560

SNAP LOCK SHEET-METAL SEAM 5 Sheets-Sheet 2 Original Filed June 1. 1964 INVENTOR Lou/s E DEMMLEE H15 Arrazusv Jan. 3, 1967 1.. F. DEMMLER 3,295,560

SNAP LOCK SHEET-METAL SEAM Original Filed June 1, 1964 5 Sheets-Sheet 4 INVENTOR Lou/5 FDEMML E H15 A rrazuev Jan. 3, 1967 1 F. DEMMLER SNAP LOCK SHEET-METAL S EAM 5 Sheets-Sheet 5 Original Filed June 1, 1964 INVENTOR [cu/5E 054041.52

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H/sArraeusv United States Patent 3,295,560 SNAP LOCK SHEET-METAL SEAM Louis F. Demmler, 431 Maple Ave., Edgewood, Pa. 15218 Continuation of application Ser. No. 374,872, June 1, 1964. This application Mar. 18, 1965, Ser. No. 444,503 9 Claims. (Cl. 138-166) This invention relates generally to lock seams connecting adjacent edges of sheet-metal elements such as found in tubular fittings and tubular enclosures having margins that follow curves or have lateral bends and are joined by lock seams and more particularly to a lock seam for connecting adjacent edge portions of sheet metal elements that follow around an arc.

This application is a continuation of application Serial No. 374,872, filed June 1, 1964..

The art of joining adjacent sheet-metal edges together in forming a seam is quite old.

Initially, some of the present lock seams of the prior art appear to be quite similar to each other. Some of the variations differentiating one lock seam from another appear to be minor but in fact are considerably different. One of the oldest seams is known as the Pittsburgh Lock Seam which is produced by a back fold and return refold with the end of the metal extending beyond the back fold to produce a pocket with a projected end. A flange member having a right angle is positioned so that the flange member enters the pocket covering the back fold and is held in place by hammering over the projected end of the pocket. The projecting end hammered over the right angle of the flange member locks the flange member in the pocket. One difliculty of this fold is that it requires the projecting end of the pocket to be hand hammered into place which produces a completed duct work that is not as neat as that of a machine formed seam. Such manual labor adds to the expense of this type joint.

One of the most popular seams is a snap lock seam that is provided with a back fold against the fiat sheet metal surface or stock and a return refold to form a pocket with an inturned back fold producing a hem. The edge of the hem does not project as far as the initial back fold. The flange is provided with a right angle bend, which flange is formed with lugs struck inwardly within the included angle so as to engage the edge of the hem when the flange is inserted in the pocket and the angle of the flange lies over the short edge of the hem.

A standard snap lock seam is formed by providing a back fold and a return refold with the edge of the metal being extended beyond the back fold and turned over the pocket to form a pocket-flange to approach the plane of the back fold. The flange for this structure is provided with a single back fold having a straight edge to engage in the angle of the pocket-flange and with an offset to engage the edge of the back fold of the pocket when the back fold of the flange is inserted into the pocket.

The next type snap lock is the same as the standard snap lock but the outwardly directed pocket-flange is provided with a back folded edge that provides stiffness and strength over that of the standard snap lock.

A snap lock seam known -as a Round Pipe snap lock is provided with a pocket having a back fold with a return refold and an inturned back fold producing a hem, the inner edge of the hem being substantially aligned with the first back fold. The flange is provided with a sharp back fold and an inturned hern raising the inner edge from the plane of the flange and producing a shoulder that would abut against the edge of the inturned hem when the flange is inserted in the pocket.

The lock seam known as the Rectangular Slide provides Patented Jan. 3, 1967 a pocket formed by an offset and back fold with a short flange toward the offset and within the seam. The flange is provided with a right angle to cover the back fold and the flange also has a back fold to form an open hem that would interlock under the hem ,of the pocket when the angle of the flange lies over the pocket back fold. This joint is termed a rectangular slide because it has to be slid longitudinally into place,

The rectangular snap seam joint provides an inturned back fold and a return refold with an indentation toward the back fold adjacent the end of the pocket. The flange member is provided with a right angle the outer end of which has a back fold producing an open hem the end of which is turned away from the flange so as to engage the indentation when slipped into the pocket.

The foregoing seams and particularly the snap lockbutton punch seam are popular and produce a neat appearance owing to the fact that the pocket is within the tubular member. However, the outstanding difiiculty with these seams is that they cannot be made or rolled in producing a curved edge asfollowing around an arc whether it is a long curve or a sharp angle transverse of the scam in tubular fitting. They may only be used in straight-away pieces and it is practically impossible to employ these snap lock-button seams in sleeves which taper or otherwise require angularbends in the seam as the tubular fitting must follow a shape from one size to another in the duct. In view of this difficulty almost every piece of ductwork o1: tubular fitting member that has an angle or a curve or a change in shape must be made by hand and cannot be rolled or otherwise prepared so that the-flange would merely enter the pocket and snap into position. The principal reason for this disadvantage in all of the snap. lock seams is the fact that they cannot be rolled by a standard slip roll forming machineso as to follow a curve or sharp angle of a short radius transverse of the seam which is invariably required in producing tubular fitting members in ductwork.

Any of the foregoing snap lock seams will either collapse or buckle when rolled in a curve or become wavy or otherwise imperfect regardless of whether it is on the outside or the inside curve of the ductwork and it is impossible to employ them for this purpose.

When the tubular fitting member is required to be formed at an angle making a sharp right angle or short radius or even an acute angle of shorter radius, or obtuse angle of longer radius the pocket of the prior art absolutely locks itself and it is impossible to insert a flange therein particularly if it has lugs. The rolled action together with the bending action will crush and misshape the pockets of the aforementioned lug snap lockseams and prevent the entry of a flange.

The principal object of this invention is the provision of a lug snap lock seam that may either follow an inside curve or an outside curve which is defined as an arc of a very long radius or may be bent to follow around a long or short radius are at either an acute angle of short radius, a right angle of longer radius, or an obtuse angle of longer radius and the pocket immediately adjacent these angles remains open to receive the lug snap locks and produces a uniform and smooth continuous surface whether it approaches the angle or follows a curve so as to provide a neat and, for the first time, a rolled seam for such tubular fitting members.

Although this rolled sheet metal lock seam for ,connecting adjacent edge portions of sheet metal elements comprising the invention is adequate for following around arcs of long and short radius arcs to produce curves, angles, or diagonals, it is also excellent for mating straight tubular members that are cylindrical or square and has improved attributes over all of the seams previously known.

Another important object of this invention is the pro vision of the use of this lock seam for securing ends on containers or for connecting the abutting ends of tubular members. These tubular members, of course, may be cylindrical or of polygon shape.- Former lock seams could not be used for this purpose because they could not be rolled into a complete circle nor could they function if the seam was sharply bent such as in a right. angle, which follow around an arc of a short radius, for use in constructing a square container with a square end. Thus as a means for fastening ends on containers or for joining the butted ends of tubular members this invention carries the snap lock seam to a new field which the former lock seams were incapable of satisfyin The novel feature of the lock seam comprising this invention is clearly brought out when the pocket is employed as the rim of. a cylindrical container and the lidis merely required to have an annular right angle flange with the I lugs carrying their abutment edges extending outwardly so that they will mate and lock with the edge of the hem in the pocket. By inserting a thin tool into the pocket and against the outer edge of the lid flange and providing a slide upwardly directly' on the bottom of the tool one need only to slide the tool in the pocket around the container to expand the throat and release each consecutive abutment edge of the lug from under the hem edge so as to remove the lid without injuring or otherwise destroying the seam. No additional lock members are necessary and the seam elements are preserved for re-use. This cannot be accomplished by the lock seams in the prior art.

Another object is the provision of a lock seam on the adjacent edges of a series of sheet metal elements which follow around an arc to provide a closure.

Another object is the provision of a lock seam wherein the lugs providing the locking for their abutment edges are gauged from the bend of the flange which provides uniformity in the seal and the strength of the lock. These abutment edges as previously stated are substantially tangent to a curved seam but would be parallel with a straight seam which represents an improvement in this invention.

Another object of this invention is the provision of a lug that produces an abutment edge on the flange that is caused to extend only the thickness of the metal for the purpose of engaging the edge of the inturned hem to lock the seam and still permit a frictional engagement between the surfaces on the opposite sides of theflange and surface of the hem on the outside of the joint and the surface of the first back fold. These surfaces form the mouth of the pocket and provide a frictional engagement with the flange to aid in sealing theduct or container and still permit the proper gauge between the abutment edges of the lugs and the bend in the flange.

The curved and angled pockets of each of these objects are made possible by a continuous offset formed by an offset bend in the edge portion of the sheet element inwardly and under and uniformly spaced from the pocket to offset the pocket relative to the surfaces of the sheet metal element as the pocket follows around the arc which may have a long radius as in a curve or a short radius as in an acute or a right angle bend.

Other objects and advantages of this invention appear hereinafter in the following description and claims.

The accompanying drawings show for the purpose of exemplification without limiting this invention or the claims thereto, certain practical embodiments illustrating the principles of this invention; wherein FIG. 1 is a view in perspective showing a tubular fitting having a one hundred and eighty degree curve employing the lock seam of this invention in each of the four corners.

FIG. 2 is an enlarged sectional view of the lock seam on the outer curve of the tubular fitting of FIG. 1.

FIG. 3. is an enlarged sectional view of the lock seam on the inner curve of the tubular fitting of FIG. 1.

FIG. 4 is a view in perspective showing a tubular fitting having one side ofl to illustrate its outer curve and inner angular bend with the lock seam of this invention in each of the four corners.

FIG. 5 is a view in perspective showing a tubular fitting having one side partially shown illustrating the outer and inner Walls formed by angles.

FIG. 6 is a perspective view illustrating a straight tubular member employed in the lock seam of this invention at diagonal corners.

FIG. 7 is a perspective view illustrating a straight tubular member employing the lock seam of this invention along only one seam in the tube.

FIG. 8 is an enlarged sectional view of the lock seam showing the flange having an offset bend to place the sheet-metal sections in alignment.

FIG. 9 is an enlarged sectional view showing the end portion straight and the pocket with a small offset to place the sheet-metal sections in alignment.

FIG. 10 is a plan view of a side of a tubular curved fitting showing the lug on the flange with its abutment surface.

FIG. 11 is a plan view of a side of a straight tubular member showing the lug on the flange with its abutment surface.

. FIG. 12 is a perspective view illustrating the lock seam of this invention as applied to a container with parts 1 shown in section.

FIG. 13 is a view illustrating the lock seam comprising this invention as applied to form a butt connection be-- tween adjacent ends of pipe with parts shown in section to illustrate the joint.

FIG. 14 is a view illustrating the lock seam comprising this invention as applied to form a butt connection between adjacent ends of tubular conduits of polygon cross section.

Referring to FIG. 1 the tubular fitting 1 is substantially semi-circular in cross section and is a tubular fitting member that is provided with curved edges to produce a 180 bend. This curved tubular fitting member 1 is provided with the top member 2 and bottom member 3 each having a marginal depending flange 4 and 5 having the series of offset outwardly struck lugs 6 each presenting only an abutment edge 7 that is accurately spaced from the inner under side 8 of the top and bottom members 2 and 3 more clearly shown in FIGS. 2 and 3. Each of the top and bottom members may be of the same size or one may be larger than the other in which case the included angle between the flanges 4 and 5 in the inner surface 8 of the top and bottom members 2 and 3 would be greater than adjacent the small member and less than 90 adjacent the top member. Such a structure would follow the same general curvature and the inner curve 10 may be the same. However, the outer curve 11 may be of smaller radius at the top than at the bottom. In other words, the joint comprising this invention is quite flexible and is readily suited to many different conditions and variations without changing or otherwise deviating from this invention.

The outside face 12 and the inside face 13 of the curved tubular fitting member 1 is provided with a marginal pocket 14 adjacent each of the curved edges 10 and 11. These pockets are readily seen in FIGS. 2 and 3 and the only difference between FIGS. 2 and 3 is the fact that the pocket 14 in FIG. 2 is formed on the upper and lower marginal edges of the outside face 12 whereas in FIG. 3 the pockets 14 are formed on the upper and lower edges of the inside face 13.

The stock or face 12 and 13 of the sheet-metal making up this invention is provided with an offset bend 15. This offset bend may be sufliciently deep to make the exterior surface of the pocket as indicated at 16 in the same plane as the outer surface 17 of the faces 12 and 13 or the offset bend may be such as to place the stock or the faces 12 and 13 in line with the depending flanges 4 and 5. The offset bend 15 is designed to be sufficiently close to the pocket without crowding the same but lending support to the pocket and is believed to be one of the important contributing factors that permits this lock seam pocket to be rolled in a curve or bent into an angle which angle may be an acute angle, a right angle, or an obtuse angle.

The pocket being offset disassociates this pocket from the stock metal permitting the entire piece to be formed into a curve without distorting, collapsing, or buckling the pocket which would prevent its use. The pockets then have an individual identity with reference to the intermediate flat sheet or curved stock metal. When these formed pockets along the edges of the flat sheet metal are passed through the standard slip roll forming machine to curve the same, these pockets being of four thicknesses of metal as compared to the single metal thickness of the adjacent free intermediate stock containing the offset between the pockets on the opposite edges of the stock are the controlling factor in the formation of the curve to produce the curved stock with one or two pockets on the fitting member.

When the pocket is formed along the edge of the stock without any offset, the flat stock controls the rolling action and the rolls actually work the pocket to crush, buckle and otherwise distort the same making it useless. This is believed to be the principal reason for the success of this invention.

When curved stock has a pocket along each of its opposite edges and isprovided with at least one offset bend in the flat stock between the pockets to make these pockets independent from each other which eliminates the effect of rigidity in the intermediate connecting flat stock when rolled by standard slip roll forming machine, proper curved sections with the snap lock pockets will be formed and will properly function.

It should be noted that the offset bend 15 extends inwardly of the tubular member and is uniformly spaced from the forward marginal edge of the pocket.

The pocket itself is provided with chamber 18 which is constructed by the outward back fold 20 (the first fold) toward the offset angle 15 and forming one side 21 of the chamber 18. The bottom of the pocket is provided with an outward refold 22 (the second fold) extending the metal away from the offset 15 and forming the opposite side 23 of the chamber 18. The end of the side 23 of the chamber 18 is provided with an inturned back fold 24 (the third fold) producing a hem 25 with its marginal edge 25 forming a locking abutment surface that is uniformly spaced from the back fold 24 thereby completing the chamber 18. The hem 25 and the first back fold 20 form the mouth to the chamber and their opposed respective surfaces 27 and 28 will be in engagement with each other owing to the spring action of the outward refold 22. When the outer marginal end 9 of the flanges 4 and 5 are forced into the mouth 30 it spreads the same for the thickness of the flanges 4 and 5 after the lugs 6 have slipped through the mouth and have their abutment edges 7 engage the edge 26 of the hem 25. At this time the marginal edge 9 of the flange could be engaging the bottom of the chamber 18 at the bend 22 for the purpose of providing a continuous seal between the flange and the chamber. However, the engagement of the marginal edge 9 of the flanges 4 and 5 with the bottom of the pocket is not necessary provided the surfaces 27 and 28 engage the opposite surfaces of the flange so as to seal the same.

It will be noted that in FIGS. 2 and 3 that the back fold which not only strengthens the spring action in maintaining the mouth 30 closed but also maintains the hem closer to the marginal edge of the pocket as defined by the back fold 20 which structural detail makes it easier to insert the flange in the pocket and far easier to employ a tool for removing the flange without undue spreading of the mouth of the pocket or otherwise injuring the interengaging and interlocking surfaces. Thus the extension of the hem back fold 24 beyond that of the first back fold 20 providing several improved advantages in the lock sea of this invention. It is obvious that one does not have to extend the marginal edge 9 of the flange to the bottom of the pocket chamber 18 and if it is so extended it will be far easier to unlock and remove the flange from the chamber of the pocket without injuring the members so that they may be re-engaged which is an important advancement in the lock seam art.

In the structure as shown in FIG. 5 the upwardly open tubular fitting member 37 is provided in its outer face 40 with two obtuse angles 38 and 39 and similar angles 41 and' 42 in its inner face 43. Here again, the corners form these obtuse angles and permit the flanges of the respective bottom and top members 44 and 45 to readily interengage in the pockets 30 and properly seal the same. With these obtuse angles it is unnecessary to notch the flanges unless at the exact bends these flanges are provided with a lug in which case it is best to notch the flange to remove the lug at the end. These structures otherwise are the same as that illustrated in each of the foregoing figures.

Referring now to FIG. 4 the rectangular cross section of the tubular fitting member 31 is designed to serve a bend. The outside face 32 follows around an are which is substantially circular and is provided with pocket members 14 at the top and bottom thereof for receiving the corresponding flanges 4 of the top member 33 and the bottom member 34. The inner face. of this tubular memher is indicated at 35 but rather than following a curve it is bent to follow around a short radius are placing the sides 35 at a 90 angle as indicated at 36. However, the pockets 14' along the marginal edges thereof are likewise bent to follow around a short radius arc in the same angle and the depending flanges 5 of the top and bottom members 33 and 34 respectively will-engage into the mouths 30 of the pockets 14 and seal the same u to the right angle bend 36. At the very apex of the bend the chamber 18 will collapse, but it will not spoil or otherwise harm the pockets 14 leading to the apex and the flanges are readily received up to this point. However, in practice it is preferable to notch the flanges 5 at the angle 36 so that the flange will not have to enter the tight angle 36 when entering the pockets adjacent this position. No other character of seam has been able to produce a joint pocket of this character which negotiates a bend following around an arc regardless of the angle of the bend.

In the structure shown in FIG. 6 the lock seam joint is illustrated as being applied to a straight tubular member 46 which is of polygon cross section and is formed by two members 47 and 48 which are duplicates of one another in that the sides 50 are provided with the pockets 14 and the sides 51 are provided with the flange members 4 as found on the end of the flange carrying the lugs 6 and bent at a right angle relative to the inner underside 8 in the same manner as that disclosed in FIG. 2. Here the pockets do not follow a curve nor do they have any bends, but they do produce a joint that is more readily opened and reclosed which is impossible by the other joints presently used which provides a very important object of this invention.

Referring now to FIG. 7 it will be noted that the lock seam is provided to engage the ends of the single piece of metal in forming a round pipe 52'. Here the pocket 14 which is constructed in the same manner as that previously described in each of the other straight structure sections. However, the flange 4 is provided with the offset 53 for the purpose of placing the exterior of the surface of the pipe on opposite sides of the joint in substantially the same cylindrical surface which is an old expediency. As previously stated this same lock seam may readily be disengaged and re-engaged without injuring or otherwise spoiling the function of the lock seam.

In the structure illustrated in FIG. 8 the pocket is the same as that previously described in each of the other structures and is positioned on the outside of the tubular member indicated at 54. However, the flange member with its flange element 4 and its lug member 6 having its abutment edge 7 is provided with an offset bend 55 which is in the direction opposite of that shown in 53 of FIG. 7. Here the offset bend 55 will center the flange 4 so that its inner surface will be in engagement with the side wall 21 of the chamber 18 in the pocket 14. This, as in all other applications, places the pocket on the outside of the member so that it may be easily operated upon so that the joint may be readily expanded and the flange removed without harm or otherwise changing the partsmaking up the joint so that it may be readily reengaged. If the joint is not intended to be opened, then the pocket could be placed on the inside of the tubular member.

Referring to FIG. 9 it will be noted that the outer surface 57, the member carrying the pocket 14, is provided with an offset bend 58 that is offset sufiiciently to align the inner surface 56 of the edge 4' with the surface on the side 28 of the pocket. The flange member in this instance is straight. Here again, the offset is employed to provide alignment with the flange, but still position the pocket 14 on the outer side of the member so that it may be opened or closed or otherwise manipulated without injury to the same. This pocket may follow around an arc because of the offset bend 58.

In the structure shown in FIG. 10 the lug 6 on the flange 4 has its abutment edge 7 disposed substantially tangent to the curve indicated at 11. This figure could be considered as a portion of the top member 2 as shown in FIG. 1.

In FIG. 11 the lug member. 60 which, provided with an abutment edge 61, is formed on the flange of the member 51 with this depending flange 4 following a straight line and having the lugs 60 formed with their abutment edges 61 parallel with the flanges as shown in FIG. 6.

Referring now to FIG. 12 the container 62 is provided with the metal bottom member 63 on the cylindrical side wall 64 having an offset as illustrated in FIGS. 1 and 2 and the pocket member 14 is the same as that previously shown, but follows around an arc that extends through 360 and is defined as a planar circular margin and its back fold 24 is in substantially the same plane as the lid 65 of the container 62. This circular pocket lies in one transverse plane and is, therefore, planar and is claimed as such. The dependent annular flange 4 is provided with a lug 6 in exactly the same manner as that shown and described with reference to FIGS. 1 and 2. To open this container, all one need do is insert a tool into the mouth 30 between the flange 4 and the inner surface 27 of the hem 25 and slide this thin tool over the lug 6 so as to clear the abutment edge 7 of the lug 6 from the corresponding engaging surface 26 of the edge of the hem. This allows the mouth 30 to open and as the tool is slid around through the mouth 30 each of the consecutive lugs will be released and raised so as to permit the lid to be opened without destruction of the pocket or the inner engaging flange.

Rather than connecting a lid to the open end of a container the same seam can be employed to connect the abutting ends of circular pipe such as illustrated at 66 and 67 as shown in FIG. 13. The end of the pipe 66 is provided with a pocket 14 which is preferably provided with the offset 15 and the end of the pipe 67 is provided with the offset 53 such as illustrated in FIG. 7 so as to place the outer surface of the pipes 66 and 67 in the readily be opened and the pipe section 66 and 67 parted without injury to the structure of the same, as shown in FIG. 13.

mounted on its end edges. 7

As illustrated in FIG. 14 the abutting ends of the pipe sections 68 and 69 are likewise provided with the external pocket member 14 that mates with a flange on the end of the pipe section 69 although this pipe is of polygonal cross section the joint may be opened in the same manner as that previously described with relation to the container of FIG. 12 or the pipe illustrated in FIG. 13. Since the butt joints such as illustrated in this view have four right angle corners owing to the fact that the polygon is either square or rectangular in cross section it is preferable to notch the flanges at the corners to also aid in the insertion of the tool for disjoining the members. The pockets 14 with their oflset 15 follow around an arc of short radius as previously described.

I claim:

1. A lock seam for connecting adjacent edge portions of sheet metal elements that follow around an arcuate margin consisting of a continuous pocket having three folds enclosing a chamber and following along one edge portion of one of said sheet metal elements, said one edge portion with said pocket following around an are, an interengaging sheet metal flange along one edge portion of another sheet metal element carrying a lock means and following around said are of said pocket and locked in said pocket to complete the lock seam, a continuous offset formed by an offset bend in said one edge portion of said sheet metal element inwardly under and immediately adjacent of said pocket to offset said pocket relative to the outer surface of said sheet metal element carrying said pocket to prevent the distortion and collapsing of said chamber, and an inturned back fold extending into said chamber and producing a hem with its marginal edge spaced uniformly from the bottom of said chamber, a mouth at the end of said chamber between the normally engaged surfaces of said inturned hem back fold and said first outward back fold, and. said lock means of said flange having abutment edges engaging said marginal hem edge in said chamber of said pocket to lock said flange in said chamber.

2. The lock seam of claim 1 characterized in that said inturned marginal hem back fold extends further from said offset bend than said first outward back fold, and a right angle bend in the sheet metal element carrying said flange to space the abutment edges of said lock means to engage said hem when said sheet metal element carrying said flange engages said first outward back fold and said right angle bend is flush with and adjacent to the bend of said inturned hem back fold.

3. The lock seam of claim 2 characterized in that said pocket and said right angle bend carrying said flange follow an outer curve on said sheet metal lock seam.

4. The lock seam of claim 2 characterized in that said pocket and said right angle bend carrying said flange follow an inner curve on said sheet metal lock seam.

5. The lock seam of claim 1 characterized in that said.

pocket and said flange follow a complete planar circular margin.

6. The lock seam of claim 2 characterized in that said pocket and said right angle bend carrying said flange This pocket also follows around an arc Here again since the pocket When cut in half longitudinally these pipe 1 sections simulate a Quonset but as would FIG. '1 when follow a complete planar circular margin with the latter forming a lid.

7. The lock seam of claim 1 characterized in that said pocket and said flange follow at least one lateral bend in said seam.

8. The lock seam of claim 1 characterized in that said flange and said pocket follow a curve and that only said abutment edges of said lock means are substantially tangent to said curve.

9. The lock seam of claim 1 characterized by a bend in said sheet metal element carrying said flange, said bend being spaced from said abutment edges to provide an offset relative to said first mentioned back fold to align the adjacent outer surfaces of said sheet metal elements on both sides of the lock seams.

References Cited by the Examiner UNITED STATES PATENTS Davidson et a1. 138166 Osborn 285424 X Cohn 138-168 X Schecter 138166 Wichner 285424 X Swett 138--163 X Pavia.

LAVERNE D. GEIGER, Primary Examiner.

T. MOORHEAD, Assistant Examiner. 

1. A LOCK SEAM FOR CONNECTING ADJACENT EDGE PORTIONS OF SHEET METAL ELEMENTS THAT FOLLOW AROUND AN ARCUATE MARGIN CONSISTING OF A CONTINUOUS POCKET HAVING THREE FOLDS ENCLOSING A CHAMBER AND FOLLOWING ALONG ONE EDGE PORTION OF ONE OF SAID SHEET METAL ELEMENTS, SAID ONE EDGE PORTION WITH SAID POCKET FOLLOWING AROUND AN ARC, AN INTERENGAGING SHEET METAL FLANGE ALONG ONE EDGE PORTION OF ANOTHER SHEET METAL ELEMENT CARRYING A LOCK MEANS AND FOLLOWING AROUND SAID ARC OF SAID POCKET AND LOCKED IN SAID POCKET TO COMPLETE THE LOCK SEAM, A CONTINUOUS OFFSET FORMED BY AN OFFSET BEND IN SAID ONE EDGE PORTION OF SAID SHEET METAL ELEMENT INWARDLY UNDER AND IMMEDIATELY ADJACENT OF SAID POCKET TO OFFSET SAID POCKET RELATIVE TO THE OUTER SURFACE OF SAID SHEET METAL ELEMENT CARRYING SAID POCKET TO PREVENT THE DISTORTION AND COLLAPSING OF SAID POCKET DUE TO THE RIGIDITY OF SAID SHEET METAL ELEMENT WHEN SAID SHEET METAL ELEMENT WITH SAID POCKET IS ROLLED INTO AN ARCUATE SHAPE, SAID POCKET HAVING A BACK FOLD OUTWARD OF SAID OFFSET AND EXTENDING TOWARD SAID OFFSET BEND AND FORMING ONE SIDE OF SAID CHAMBER, AND A REFOLD OUTWARD OF SAID OFFSET AND EXTENDING AWAY FROM SAID OFFSET BEND AND FORMING THE BOTTOM AND THE OTHER SIDE OF SAID CHAMBER, AND AN INTURNED BACK FOLD EXTENDING INTO SAID CHAMBER AND PRODUCING A HEM WITH ITS MARGINAL EDGE SPACED UNIFORMLY FROM THE BOTTOM OF SAID CHAMBER, A MOUTH AT THE END OF SAID CHAMBER BETWEEN THE NORMALLY ENGAGED SURFACES OF SAID INTURNED HEM BACK FOLD AND SAID FIRST OUTWARD BACK FOLD, AND SAID LOCK MEANS OF SAID FLANGE HAVING ABUTMENT EDGES ENGAGING SAID MARGINAL HEM EDGE IN SAID CHAMBER OF SAID POCKET TO LOCK SAID FLANGE IN SAID CHAMBER. 